In the injection molding process, a polymer can be subjected to high temperatures for extended periods of time. Since many of the mechanical and toughness properties of the molded article depend on the molecular weight of the polymer, it is desirable for the polymer to have excellent melt stability or retention of molecular weight during melt processing. Polycarbonates are a class of polymers which exhibit a relatively high retention of molecular weight when injection molded. A known method for maintaining high molecular weight during the processing of polyesters, copolyesters, and blends thereof is to compound selected antioxidants, one of which is usually a phosphite, into the formulation.
U.S. Pat. No. 4,391,954 by Scott, dated Jul. 5, 1983, describes a compatible composition consisting essentially of (a) a nonhalogenated aromatic polycarbonate derived from bisphenol-A and (b) a polyester component consisting of amorphous polyester solely derived from 1,4 cyclohexanedimethanol and a mixture of iso- and terephthalic acids.
U.S. Pat. No. 4,786,692 by Allen, et al, dated Nov. 22, 1988, describes a thermoplastic composition comprising a blend of an aromatic polycarbonate and a copolyester derived from a glycol portion comprising 1,4 -cyclohexanedimethanol and ethylene glycol present in molar ratios of 1:4 to 4:1, respectively, and an acid portion comprising an aromatic dicarboxylic acid selected from terephthalic acid, isophthalic acid, and mixtures thereof.
U.S. Pat. No. 4,188,314 by Fox et al. dated Feb. 12, 1980, describes a shaped article comprising an aromatic polycarbonate and a thermoplastic polyester derived from 1,4-cyclohexanedimethanol and a mixture of iso- and terephthalic acids.
EPO Application No. 88119330, Publication Number 0 320 658, date filed, Nov. 21, 1988, describes an admixture of an aromatic polycarbonate with an anti-yellowing effective amount of a certain phosphite.
Many of these disclosures include the incorporation of stabilizers in the description of the invention; however, they do not disclose the use and unexpected benefits of combinations of aliphatic and aromatic phosphite compounds.